PRETREATMENT METHOD OF NITRIDED PARTS OF ALLOY CAST IRON WITH SPHEROIDAL GRAPHITE Russian patent published in 2008 - IPC C21D1/78 C21D5/00 C23C8/02 G01R33/12 

FIELD: processes for heat treatment of cast iron parts with spheroidal graphite.

SUBSTANCE: method comprises steps of testing initial structure by means of coercive force meter and selecting heat treatment modes on base of testing results. Parts are subjected to austenization at 880 - 930°C; interim cooling of parts in furnace till temperature in range Ar₃ - Ar₁ ; cooling at rate 5 -10°C per minute till temperature in range between temperature of starting A - P conversion and temperature exceeding by 50°C maximum-stability of temperature of austenite being converted to upper bainite or troostite. Then part is subjected to isothermal soaking at such temperature till maximally possible degree of A - P conversion. After cooling structure is inspected by means of coercive force meter for detecting tendency of pearlite and tempered bainite to changes at further nitriding. Depending upon inspection results tempering mode is selected and after such tempering final testing of structure by means of coercive force meter is realized according to index values of scale developed on base of investigating relationship of readings of coercive force meter from initial structure and its changes at nitriding process and also from growth and warping of parts at nitriding.

EFFECT: possibility for producing stable structure resistant against changes at nitriding process.

2 cl, 1 ex